UUIDGenerator.java

/**
 *  OpenKM, Open Document Management System (http://www.openkm.com)
 *  Copyright (c) 2006-2011  Paco Avila & Josep Llort
 *
 *  No bytes were intentionally harmed during the development of this application.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *  
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

package com.openkm.util;

import java.net.InetAddress;

/**
 * @author martin
 *
 * Very simple UUID generator based in Hibernate implementation
 */
public class UUIDGenerator {
	private static final int IP;
	static {
		int ipadd;
		try {
			ipadd = toInt( InetAddress.getLocalHost().getAddress() );
		} catch (Exception e) {
			ipadd = 0;
		}
		IP = ipadd;
	}
	private static short counter = (short) 0;
	private static final int JVM = (int) ( System.currentTimeMillis() >>> 8 );
	
	/**
	 * Unique across JVMs on this machine (unless they load this class
	 * in the same quater second - very unlikely)
	 */
	private static int getJVM() {
		return JVM;
	}
	
	/**
	 * Unique in a millisecond for this JVM instance (unless there
	 * are > Short.MAX_VALUE instances created in a millisecond)
	 */
	private static short getCount() {
		synchronized(UUIDGenerator.class) {
			if (counter<0) counter=0;
			return counter++;
		}
	}
	
	/**
	 * Unique in a local network
	 */
	private static int getIP() {
		return IP;
	}
	
	/**
	 * Unique down to millisecond
	 */
	private static short getHiTime() {
		return (short) ( System.currentTimeMillis() >>> 32 );
	}
	
	private static int getLoTime() {
		return (int) System.currentTimeMillis();
	}
	
	public static String generate(Object obj) {
		StringBuffer buffer = new StringBuffer(36)
		.append(getIP())
		.append(getJVM())
		.append(getHiTime())
		.append(getLoTime())
		.append(getCount());
		
		if (buffer.charAt(0) == '-') {
			buffer.deleteCharAt(0);
		}
		return buffer.toString();
	}
	
	public static int toInt( byte[] bytes ) {
		int result = 0;
		for (int i=0; i<4; i++) {
			result = ( result << 8 ) - Byte.MIN_VALUE + (int) bytes[i];
		}
		return result;
	}
}